This invention relates to improving the adhesion of water-based inks to polyolefin polymers. In particular this invention is directed to improving the printing of polyolefin films with water-based inks. An important aspect of the present invention is the improved adhesion of water-based inks to polyolefin films containing N-ethanol erucamide and/or N-ethanol oleamide.
Olefin homopolymers and copolymers are of commercial importance for the manufacturer of numerous articles such as films and other items. In order to be useful for many of these functions it is desirable that the polyolefinic composition have good slip characteristics. This can be determined by measuring the coefficient of friction of the polyolefin. It is of increasing importance that the polyolefinic composition have excellent adhesion to water-based inks.
In order to obtain a satisfactorily low coefficient of friction, often slip agents are added to the polyolefin to lower its coefficient of friction below about 0.5, preferably below 0.3. Many slip agents and other additives for polyolefins are disclosed in the literature. These additives will lower the coefficient of friction of the polyolefin to desired levels, permitting ready handling of shaped articles and films prepared from the polyolefinic material. Polyolefinic polymers having poor slip characteristics are difficult to handle when the polymer is manufactured in the customary manner of large rolls. During storage and subsequent processing, the low slip films tend to adhere layer to layer. Also such films can encounter large frictional forces in processing equipment that often cause distortions and even tearing of the film, especially when using thin film.
Rowland et al U.S. Pat. No. 2,956,979 discloses inhibiting the blocking tendencies of polyethylene by introducing into the composition a small amount of an alkylol amide of the structural formula: ##STR1## wherein R is a saturated aliphatic acyl radical of from about 18 to about 30 carbon atoms and R' is an alkyl radical group of 1 to 6 carbon atoms. Toy et al U.S. Pat. No. 3,028,355 discloses the use of diatomaceous earth to reduce the tendency of polyethylene to block. Haeske et al U.S. Pat. No. 3,266,924 discloses the blending of a mixture of finely divided siliceous material and a fatty acid amide slip agent into polyethylene to enhance its slip and blocking properties. Ross et al U.S. Pat. No. 3,326,840 discloses the incorporation of a small amount of a mono-N-substituted saturated carboxylic acid amide of the formula: ##STR2## wherein R is an aliphatic acyl radical having from 12 to 30 carbon atoms and R' is an aliphatic group having from 1 to 6 carbon atoms, especially an alkylol group, into a copolymer of ethylene and an aliphatic ethylenically unsaturated carboxylic ester to improve its resistance to blocking and improve its slip properties.
Foster U.S. Pat. No. 3,647,738 discloses blending an amide having the formula: ##STR3## wherein R is an alkenyl radical having 18 to about 22 carbon atoms and R' is a divalent hydrocarbon radical containing 3 to 5 carbon atoms with an alpha-olefin polymer composition to provide compositions having low blocking and no bloom characteristics and high slip properties.
Wharton U.S. Pat. No. 3,396,137 discloses compositions comprising an ethylene polymer and an N-substituted unsaturated carboxylic amide having improved properties with respect to the coefficient of friction and the adhesion of solvent-based printing inks to the surface of the polymer.
While the foregoing patents and other literature disclose a variety of additives that improve the slip and/or blocking properties of polyolefins, they are silent on improving the adhesion of water based inks to said polyolefins. It is necessary that the polyolefinic compositions containing the slip and blocking agents have excellent ink adhesion, particularly to water based inks and good printability so that the molded article, film or other item made from the polymer can be suitably printed. Of late it has become highly desirable for environmental reasons, such as to reduce emissions of volatile organic compounds, that the inks used to print on the polyethylene composition be water-based inks.
Accordingly it is an object of the present invention to improve the slip properties of polyolefinic compositions and simultaneously improve the ink adhesion properties, particularly the adhesion of water-based inks.
It is another object of the present invention to improve the printability of water-based inks on polyolefinic compositions, particularly on films and bags used as packaging material.
Another object of the present invention is to impart the desired slip, printability and adhesion to water-based inks to polyolefin compositions without adversely affecting the optical properties of the polyolefin.
Other objects of the present invention will become apparent from the ensuing description.